It has already been proposed, in the case of Hook's joints, to provide the arms of the cross member with grooves by subjecting the arms to a roughing operation while being turned to permit the storage of grease in the grooves (GB-A 2117088).
The disadvantage of the above proposal consists in that in view of the line contact existing between the arms and the needles of a needle bearing arranged thereon, a defined surface is not available. The load is applied via an interrupted line contact, and the area pressure fluctuates as a function of the distribution of the grooves.
It is also known to press or forge a workpiece by means of a two-part tool (DE-OS 2 107 459). To avoid any pressing or forging burr, the above publication proposes to measure the amount of material in such a way that no forging or pressing burr occurs during production. However, the disadvantage of this proposal is that it is not possible to measure the material that accurately so that either some pressing or forging burr occurs, even if it is just a very small amount, or the die is not completely filled so that in the final analysis the workpiece does not have the required shape.
It is the object of the present invention to design the arms of a constant velocity universal joint of the tripode type in such a way as to improve the distribution of area pressure under torque loads and, furthermore, to provide a free space for storing grease.
It is a further object of the present invention to design a journal-shaped workpiece with a convexly curved outer circumference in such a way that any pressing or forging burr is located in a position which does not adversely affect the subsequent use of the workpiece and that there is no need for subsequent machining.
In accordance with the invention, one objective is achieved in that, at their ends facing the two directions of rotation of the joint, the arms are each provided with a generally flat face which extends parallel to the longitudinal axis of the joint and to the axis of the respective arms.
By providing this face, the circumferential force depending on the torque transmitted is divided into two equal force components. As a result, the area pressure values are reduced.
At the same time, the free space formed by this face and the enveloping cylinder associated with the arm serves as a storage space for lubricating grease.
In addition, this measure reduces the noise of the joint.
In accordance with the present invention, a further objective is achieved in that on both sides, the region of the burr of the arms is located on this generally flat face where the outer contour is pulled radially inwardly, with the flat portions being formed in the respective locations.
The design in accordance with the present invention is advantageous in that bearing rings may be positioned on the journal-shaped workpiece without there being any need for any subsequent machining.
In an advantageous embodiment of the present invention it is proposed that in the case of an inner joint part of a tripode joint produced by forming and comprising radially outwardly pointing tripode arms serving to receive rollers, the flat portions are provided at the tripode arms.
In this way, any subsequent machining of the inner joint part carrying the tripode arms is avoided.
In the case of a process of forming a workpiece which is produced by a two-part forming tool, which is journal-shaped and which, when shown in an axial section, comprises a convexly curved outer circumference, the flat portions are provided at the journal-shaped workpiece during the forming operation as a result of the two-part forming tool being shaped accordingly.
In this way it is possible to provide the flat portions in a simple and cost-effective way.
According to one embodiment of the invention, the faces are provided on cylindrically shaped arms.
According to a further feature of the invention, the faces are provided on spherically shaped arms.
The arms of tripode joints are normally either cylindrical or spherical.
Both types benefit from the advantages of the invention.
According to an advantageous embodiment of the invention it is proposed that in the case of a joint with part-cylindrical guiding tracks, the spherically shaped outer face of the outer roller is provided with a concentrically arranged, rotating, cylindrically shaped face and that the center plane of the outer roller extending perpendicularly relative to the axis of the arm at the same time constitutes the center plane of the face.
Additionally, with this embodiment, the fact that the outer roller of the roller assembly is supported in the guiding grooves of the outer joint part is utilized to split the circumferential force into two force components.
According to an advantageous feature of the invention, it is proposed that, in the case of a joint whose inner roller is provided with a spherical inner wall, the inner roller may be guided over the spherical arm as a result of an elastic, radially inwardly directed deformation caused by said roller being loaded by a force F extending perpendicularly to the faces.
In addition to the advantages already mentioned, this embodiment is advantageous in that an inner roller with a spherical inner wall can easily be mounted on a spherical arm without causing an design-related additional expenditure.
In an advantageous embodiment of the present invention, the journal-shaped workpieces are produced by forging.
In a further advantageous embodiment of the present invention, the journal-shaped workpieces are produced by pressing.
In an advantageous application of the process, the flat portions are provided at the arms of the inner joint part.
According to a further feature of the process, the flat portions are provided at an outer roller for the purpose of guiding the arms of an inner joint part.
This design makes it possible to produce the inner part of a tripode joint in a simple and cost-effective way.